In this study, the effects of using pure water, water/ethylene glycol mixture with 50:50 wt% and pure ethylene glycol as the working fluids on the energy and exergy efficiencies of a photovoltaic thermal (PVT) system are experimentally investigated. Moreover, the performance of the PVT systems are compared with a conventional photovoltaic (PV) system. The experiments are performed on a selected day in August at the Ferdowsi University of Mashhad, Mashhad, Iran (Latitude: 36° and Longitude: 59°). The investigated parameters in this study are: the photovoltaic cells temperature; output electrical and thermal powers; electrical and thermal energy efficiencies; output electrical and thermal exergies; and electrical and thermal exergy efficiencies. Based on the results, the PVT system with water/ethylene glycol mixture increases the output electrical power by about 5.41 % compared to that of the PV system. Furthermore, the results indicate that using pure water in the PVT system enhances electrical and thermal energy efficiencies compared to those of pure ethylene glycol and water/ethylene glycol mixture, whereas the overall exergy efficiency of PVT systems with pure water and water/ethylene glycol mixture working fluids are approximately same.